Drafted 112th overall by the NY Islanders in the 1974 NHL Entry Draft, Langevin instead chose to sign with the Edmonton Oilers of the rival World Hockey Association (who also had selected him in the WHA draft the same year) since his prospects of getting regular playing time were better in the WHA. Langevin became a solid performer for the Oilers, making the WHA Second All Star team in 1978–79. When the Oilers joined the NHL the following season, the Islanders reclaimed him as a former New York draft pick.

Langevin was a strictly defensive defensemen, whose forte was full-body checking. Langevin was instrumental in the Islanders come-back victory in the 1985 playoffs against the Washington Capitals. Benched for the first two losses, he entered game three with a decisive physical presence, most notably checking sniper Mike Gartner with a powerful hip check. The Islanders went on to win three straight and became the only team ever to lose the first two games of a 5 game series and go on to win.

Langevin served as head coach of the expansion WCHLIdaho Steelheads during the 1997–98 season. After a single season in Idaho he returned to Minnesota and became a real estate appraiser and high school hockey coach. He also served as a South Suburban (MnJHL) head coach until the team folded following the 2001–02 season. He has also done part-time work for the NHL's Central Scouting Service after his retirement.

Langevin, who wore #26 for the Islanders, was inducted into the U.S. Hockey Hall of Fame in 1993.